High-pressure sensors are utilized in many systems such as in automation technology and in the automotive field. In the automotive field, the high-pressure sensors are used in gasoline-direct injection, common rail diesel-direct injection, electronic stability programs and in electro-hydraulic brakes, among others.
In addition to capacitive measuring methods for pressure sensors, piezoresistive methods are known where, for instance, metal resistors are interconnected in the form of a Wheatstone bridge on a suitably designed steel membrane. Elastic elongation or compression of the resistors produces detuning of the bridge, the detuning generating a measured variable which represents the applied pressure. In applications in the motor vehicle field, for instance, such high-pressure sensors are required to have high sensitivity, i.e., the highest possible change in resistance in response to occurring mechanical deformations (high k factor). Furthermore, the high-pressure sensors must exhibit high temperature stability from at least −40° C. to +140° C. so as to be suitable for use in different regions of the motor vehicle. In addition, the highest possible stability must be achieved over the service life of the sensor, a period of approximately ten years being provided in motor vehicle applications. Moreover, in special applications such as detection of the combustion-chamber pressure, even higher temperature resistances of up to approximately 400° C. are demanded.
From the U.S. Pat. No. 4,876,893, a pressure sensor is already known which has a resistance layer for measuring the pressure, this layer being made of nickel, chromium and silicon. In the not prepublished-document German Patent Application No. 103 14 770, the production of a piezo-sensitive pressure sensor is described where the piezoelectrical properties of a resistance layer are improved by suitable environmental conditions.
A description of the partial crystallization of an NiCr(Si) layer has been provided by Bruckner et al. in the Journal of Applied Physics, vol. 87, no. 5, on page 2219 ff. In sensors that have NiCr(Si) layers, an offset drift may be encountered in an electrostatic discharge (ESD). This noticeable vulnerability of the measuring accuracy in sensors of this type constitutes an intrinsic characteristic of the utilized resistance layer, as it is described, for instance, by Wang et al. in “Power Dissipation of Embedded Resistors” in IPC Printed Circuits Expo 2003.